1. Field of the Invention
The present invention relates to a transmitting/receiving system for transmitting/receiving an audio signal, and a transmitting device and a device including a speaker, which are used in this transmitting/receiving system.
2. Description of the Related Art
Audio/visual (A/V) systems which have two or more audio channels and which can create a reproduced sound field producing a sense of presence have come into use. For example, in a home theater system or the like that uses a DVD (digital versatile disk) player, audio channels are provided in a form, such as 5.1 channels or 6.1 channels, that is, a so-called “multichannel system (multichannel audio processing system)”.
In a 5.1-channel system, six audio channels respectively correspond to a left (L) speaker, a right (R) speaker, and a center (C) speaker which are provided in front of a user, and a surround left (SL) speaker, a surround right (SR) speaker, and a subwoofer which are provided behind the user. In a 6.1-channel system for seven audio channels, an audio channel for a surround center (SC) speaker is added to 5.1 channels. The representation “0.1” in each of the 5.1 channels and 6.1 channels represents a channel for a subwoofer.
In a multichannel system of the above type, when a reproducer or an amplifier is connected to speakers corresponding to channels by using cables, it may take a long time to wire and connect cables, and wired cables may become obstructive.
Accordingly, for example, various types of cordless systems that use infrared radiation and FM (frequency modulation) signals to transmit audio signals from sound sources to speakers have been proposed. These cordless systems include those in which, when sounds must be selectively reproduced only from particular speakers, by diving a carrier frequency by the required number, and establishing correspondence for each divided carrier frequency between particular transmitting and receiving ends, volume, etc., can be separately controlled.
Japanese Unexamined Patent Application Publication No. 06-120903 discloses a technology directed to a cordless system using infrared radiation. In this technology, by controlling an infrared radiation direction and range without using a plurality of carrier frequencies, audio signals are transmitted only to particular speakers. By using the technology in Japanese Unexamined Patent Application Publication No. 06-120903, a circuit configuration of a transmitting unit can be simplified compared with the case of using a plurality of frequencies. This can reduce an increase in cost.
As described above, by using a multichannel system of a cordless type, problems, such as time-consuming cable wiring and connection and obstructive wired cables, can be eliminated, and a reproduced sound field producing a sense of presence can be easily created.
However, in a case in which a multichannel system does not perform multichannel reproduction, for example, when a multichannel system for 5.1 channels reproduces only sounds on two channels (right and left), speakers for four channels, which include a subwoofer, are not used and become useless.
In this case, it is possible that the speakers unused for reproduction be used in a different sound reproducing system. However, in order to use the unused speakers in the different sound reproducing system, the operation of connecting a device that sends an audio signal and the speakers is required. This may trouble the user.
As described above, even if plural speakers dedicated for a multichannel system are installed, there is a possibility that all the plural speakers may not be used, and effective use of the speakers may trouble the user. In addition, even if, in a relatively small room, the user listens to reproduced monaural sound or two-channel stereo sound, there is a need to preferably realize, as easily as possible and with less cost, a reproduced sound field producing a sense of presence as much as possible.